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Embryology
Embryology is the study of the development of an embryo. An embryo is defined as any organism in a stage before birth or hatching. Embryology is of significance to psychologists for a number of reasons:- *It is the process by which genetic instructions are reproduced in anatomical form *The process illuminates interesting relationships between physical structures that are derived from the same initial material. *William Sheldon in his theory of somatotypes understood that body types arose through embrological processes and that particular organizations of anatomical structures gave individuals different needs and constitutions which he felt were reflected in personality types *[[Embryology is the study of the development of an embryo. An embryo is defined as any organism in a stage before birth or hatching. Embryology refers to the development of the fertilized egg cell (zygote) and its differentiation into tissues and organs. After cleavage, the dividing cells, or morula, becomes a hollow ball, or blastula, which develops a hole or pore at one end. In animals, the blastula develops in one of two ways that divides the whole animal kingdom into two halves. If in the blastula the first pore (blastopore) becomes the mouth of the animal, it is a protostome; if the first pore becomes the anus then it is a deuterostome. The protostomes include most invertebrate animals, such as insects, worms and molluscs, while the deuterostomes includes more advanced animals including the vertebrates. In due course, the blastula changes into a more differentiated structure called the gastrula. The gastrula with its blastopore soon develops three distinct layers of cells (the germ layers) from which all the bodily organs and tissues then develop: * The innermost layer, or endoderm, gives rise to the digestive organs, lungs and bladder. * The middle layer, or mesoderm, gives rise to the muscles, skeleton and blood system. * The outer layer of cells, or ectoderm, gives rise to the nervous system and skin. In humans, the term embryo refers to the ball of dividing cells from the moment the zygote implants itself in the uterus wall until the end of the eighth week after conception. Beyond the eighth week, the developing human is then called a fetus. Embryos in many species often appear similar to one another in early developmental stages. The reason for this similarity is because species have adapted into the environment of pregnancy. These similarities among species are called analogous structures, which are structures that have the same or similar function and mechanism, but evolved separately. Vertebrate and invertebrate embryology Many principles of embryology apply to both invertebrate animals as well as to vertebrates. Parker, Sybil. "Invertebrate Embryology," McGraw-Hill Encyclopedia of Science & Technology (McGraw-Hill 1997). Therefore, the study of invertebrate embryology has advanced the study of vertebrate embryology. However, there are many differences as well. For example, numerous invertebrate species release a larva before development is complete; at the end of the larval period, an animal for the first time comes to resemble an adult similar to it parents. Although invertebrate embryology is similar in some ways for different invertebrate animals, there are also countless variations. For instance, while spiders proceed directly from egg to adult form many insects develop through at least one larval stage. Modern embryology research Currently, embryology has become an important research area for studying the genetic control of the development process (e.g. morphogens), its link to cell signalling, its importance for the study of certain diseases and mutations and in links to stem cell research. See also *Cell signalling *Developmental biology *Embryogenesis *Epigenesis (biology) *Germ layers *Hedgehog signaling pathway *Morphogens *Neuroectoderm *Ontogeny *Prenatal development *Recapitulation theory *William Sheldon Footnotes References * UNSW Embryology Large resource of information and media * http://www2.merriam-webster.com/cgi-bin/mwmednlm?book=Medical&va=embryo Definition of embryo according to Webster Further reading * Scott F. Gilbert. Developmental Biology. Sinauer, 2003. ISBN 0-87893-258-5. * Lewis Wolpert. Principles of Development. Oxford University Press, 2006. ISBN 0-19-927536-X. External links * Embryo Research UK philosophy and ethics website discussing the ethics of embryology * Human embryo research Canadian website covering the ethics of human embryo research * University of Indiana's Human Embryology Animations *''The Developing Human (Keith L.Moore'') http://www.youtube.com/watch?v=Rb0uZefwQnc *